Relapse of Clostridiumdifficile occurs in 10 to 25 percent of patients treated with metronidazole or vancomycin. Furthermore, multiple relapses in the same patient are common and up to 10 or more bouts of relapsing colitis have occurred in some patients. Cumulative experience from case series and controlled trials shows that fecal microbiota transplantation (FMT) is effective when used to treat relapsing C. difficile infection (CDI) [1,2] and has been evaluated for treatment of irritable bowel syndrome, obesity, and inflammatory bowel disease [3-6].

The gastrointestinal tract harbors a stable, highly complex community of microorganisms, which exists in symbiosis with the host. The human gut microbiota is estimated to consist of as many as 1000 to 1200 bacterial species and at least 1014 bacteria, most of which are in the colon [7]. The beneficial roles mediated by the microbiota for the host include the synthesis of vitamins, the fermentation of dietary carbohydrates, the metabolism of bile and host hormones, and competitive exclusion ("colonization resistance") of pathogens taking residence in the gut community [8]. The microbiota also influences the development and maturation of the immune system through interactions with the gut epithelium [9,10].

The composition of the microbiota is significantly affected by the extensive use of antibiotics, which could lead to a selective removal of a group of bacteria species that serve as a barrier to colonization and/or persistence of pathogens [11,12]. Antibiotic-mediated changes in the composition of the gut microbiota may also lead to homeostatic imbalance through alterations in the gut barrier functions and result in mucosal immune defects, which would predispose the host to enteric infections such as C. difficile by allowing environmentally acquired spores to germinate and successfully colonize the gut [13].

Although specific antimicrobial therapy is effective against C. difficile infection (CDI), recurrence of CDI is an increasing problem following therapy. Recurrent C. difficile is associated with a decrease in fecal microbial diversity deficient in Bacteroidetes and Firmicutes,both of which generally dominate within the gut microbiota [14,15]. Transplantation of stool microbiota from healthy individuals to patients with recurrent C. difficile restores thesestrains and breaks the cycle of recurrence [16-19].

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Important information about IND requirements for use of fecal microbiota to treat Clostridium difficile infection not responsive to standard therapies. US Food and Drug Administration. Available at: http://www.fda.gov/BiologicsBloodVaccines/NewsEvents/WorkshopsMeetingsConferences/ucm357258.htm (Accessed on June 25, 2013).